1. Field of the Invention
The present invention relates to a lens white-turbid state diagnostic apparatus for diagnosing a white turbid state of a lens of a camera, which is caused by impurities deposited by drying out water attached to a surface of the lens.
2. Description of the Related Art
Recently, for a vehicle such as an automobile, vehicle periphery recognition systems have been in practical uses. In such a vehicle periphery recognition system, a camera is installed on a vehicle to image a periphery of the vehicle and the system detects a position of another vehicle, a position of a lane marker, or a position of a driving lane from an obtained image, and judges a possibility of contact with the another vehicle or a possibility of a lane departure to alert a driver.
In such a system, for example, while driving in the rain, water splashed by the vehicle can be attached to a lens surface of the camera. Also, while driving on a dirt road, dust stirred up by the vehicle can be attached to the lens surface of the camera. Further, while driving on a road where a snow-melting agent is spread, the snow-melting agent splashed by the vehicle can be attached to the lens surface of the camera. Those substances attached as described above are dried, and impurities in water, dust, or snow-melting agent are deposited and piled up on the lens surface to cause grime (hereinafter, white turbidity) on the lens surface.
When a white turbid part is generated on the lens surface, light entering the lens is scattered at the white turbid part and therefore blur or bleed occurs in the observed image. Since images of other cars or lane markers to be detected are deformed because of the blur or bleed, detection failure (no detection) of the other cars or lane markers or detection of non-existing other car or lane marker (false detection) occurs. Due to the occurrence of the detection failure or false detection, an appropriate alert to the driver may not be provided.
In a system where crews in the vehicle cannot visibly recognize the image obtained by the camera, the crews cannot confirm that the lens has a white-turbid part, and therefore the above detection failure or false detection gives the crew with a sense of uncertainty to the system.
A method as a technology for detecting a grime on a lens is disclosed (see, for example, Japanese Patent Application Publication 2003-259358), in which a plurality of images are photographed at different timings, differences between the plurality of images are accumulated, and a region having a gray value (an accumulated value of the differences) which is a predetermined value or less and having an area which is a predetermined area value or more is detected as a grime on the lens.
In a grime detection device disclosed in Japanese Patent Application Publication 2003-259358, the grime on the lens is detected based on the differences in the plurality of images photographed at different timings. In detection, the region is detected, where the accumulated value of the differences is the predetermined value or less, and the area is the predetermined area value or more.
However, in the grime detection device disclosed in Japanese Patent Application Publication 2003-259358, in a plurality of images photographed at different timings, a region having small variation in gray values, such as a region of a dirt road or a uniform asphalt pavement surface in addition to a grime can be detected as a grime and therefore it is difficult to steadily detect only a grime on a lens.